Environmental measurements were also collected, to track pollution levels and volunteers' exposure. When exercising it's best to avoid highly-polluted areas, swapping them for green spaces or even back streets where pollution is lower.
The project was again led by researchers from Imperial College London alongside Duke University. Two-thirds of the volunteers had been diagnosed with either heart disease or chronic obstructive pulmonary disease (COPD), while the others were healthy (no pre-existing heart or lung condition).
Participants were randomly assigned to spend two hours walking along the western end of London's Oxford Street, an area where traffic is restricted to diesel-powered buses and cabs; or through a traffic-free area of the city's Hyde Park.
Although the team noted that stress could be a contributing factor, with the increase in noise and the number of people on Oxford Street another reason behind the physiological differences observed, the new findings still add to the growing body of evidence on the dangers of urban air pollution.
On Oxford Street, pollution including black carbon, nitrogen dioxide, and fine particulate matter regularly exceeds air quality limits set by the World Health Organization (WHO).
In comparison, when they walked in Hyde Park "all participants, irrespective of their disease status..."
After analyzing the results, they found those who paraded around Hyde Park saw significant lung capacity improvement within the first hour of exercise, which often lasted for more than 24 hours.
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Oxford Street walkers who were healthy only had a 4.6 percent drop, coronary heart disease subjects saw 16 percent dip and those with ischemic heart disease only experienced a 8.6 percent reduction. "It shows that we can't really tolerate the levels of air pollution that we now find on our busy streets".
"Our data indicates that taking medications which improve arterial stiffness such as statins, ACE inhibitors, and calcium channel blockers may well reduce the adverse effects of air pollution in individuals with ischaemic heart disease", says Prof Chung. The results may or may not be applicable to people living elsewhere.
Scientists from Imperial College London measured the health boosts that people aged over 60 received from brisk walks in different parts of London.
"Exercise is crucial in reducing the risk of a heart attack or stroke, but it seems risky levels of air pollution could be erasing these benefits in older adults". The negative effect may well be the same in younger people, say the authors, and it reinforces the urgency of reducing emissions in city streets.
"As long as American automakers drag their feet on fuel standards and other sustainability regulations, they're showing that they care more about their short-term financial interests than they do about long-term benefits for public health, the planet, and even the economy", she said.
"For many people, such as the elderly or those with chronic disease, the only exercise they very often can do is to walk", Chung said.
'Our research suggests that we might advise older adults to walk in green spaces, away from built-up areas and pollution from traffic'. "But for those living in inner cities, this may be hard to do, and there may be a cost associated with it as they have to travel further away from where they live or work".